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  22. <h1><tt>ffi.*</tt> API Functions</h1>
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  65. <div id="main">
  66. <p>
  67. This page describes the API functions provided by the FFI library in
  68. detail. It's recommended to read through the
  69. <a href="ext_ffi.html">introduction</a> and the
  70. <a href="ext_ffi_tutorial.html">FFI tutorial</a> first.
  71. </p>
  72. <h2 id="glossary">Glossary</h2>
  73. <ul>
  74. <li><b>cdecl</b> &mdash; An abstract C&nbsp;type declaration (a Lua
  75. string).</li>
  76. <li><b>ctype</b> &mdash; A C&nbsp;type object. This is a special kind of
  77. <b>cdata</b> returned by <tt>ffi.typeof()</tt>. It serves as a
  78. <b>cdata</b> <a href="#ffi_new">constructor</a> when called.</li>
  79. <li><b>cdata</b> &mdash; A C&nbsp;data object. It holds a value of the
  80. corresponding <b>ctype</b>.</li>
  81. <li><b>ct</b> &mdash; A C&nbsp;type specification which can be used for
  82. most of the API functions. Either a <b>cdecl</b>, a <b>ctype</b> or a
  83. <b>cdata</b> serving as a template type.</li>
  84. <li><b>cb</b> &mdash; A callback object. This is a C&nbsp;data object
  85. holding a special function pointer. Calling this function from
  86. C&nbsp;code runs an associated Lua function.</li>
  87. <li><b>VLA</b> &mdash; A variable-length array is declared with a
  88. <tt>?</tt> instead of the number of elements, e.g. <tt>"int[?]"</tt>.
  89. The number of elements (<tt>nelem</tt>) must be given when it's
  90. <a href="#ffi_new">created</a>.</li>
  91. <li><b>VLS</b> &mdash; A variable-length struct is a <tt>struct</tt> C
  92. type where the last element is a <b>VLA</b>. The same rules for
  93. declaration and creation apply.</li>
  94. </ul>
  95. <h2 id="decl">Declaring and Accessing External Symbols</h2>
  96. <p>
  97. External symbols must be declared first and can then be accessed by
  98. indexing a <a href="ext_ffi_semantics.html#clib">C&nbsp;library
  99. namespace</a>, which automatically binds the symbol to a specific
  100. library.
  101. </p>
  102. <h3 id="ffi_cdef"><tt>ffi.cdef(def)</tt></h3>
  103. <p>
  104. Adds multiple C&nbsp;declarations for types or external symbols (named
  105. variables or functions). <tt>def</tt> must be a Lua string. It's
  106. recommended to use the syntactic sugar for string arguments as
  107. follows:
  108. </p>
  109. <pre class="code">
  110. ffi.cdef[[
  111. <span style="color:#00a000;">typedef struct foo { int a, b; } foo_t; // Declare a struct and typedef.
  112. int dofoo(foo_t *f, int n); /* Declare an external C function. */</span>
  113. ]]
  114. </pre>
  115. <p>
  116. The contents of the string (the part in green above) must be a
  117. sequence of
  118. <a href="ext_ffi_semantics.html#clang">C&nbsp;declarations</a>,
  119. separated by semicolons. The trailing semicolon for a single
  120. declaration may be omitted.
  121. </p>
  122. <p>
  123. Please note that external symbols are only <em>declared</em>, but they
  124. are <em>not bound</em> to any specific address, yet. Binding is
  125. achieved with C&nbsp;library namespaces (see below).
  126. </p>
  127. <p style="color: #c00000;">
  128. C&nbsp;declarations are not passed through a C&nbsp;pre-processor,
  129. yet. No pre-processor tokens are allowed, except for
  130. <tt>#pragma&nbsp;pack</tt>. Replace <tt>#define</tt> in existing
  131. C&nbsp;header files with <tt>enum</tt>, <tt>static&nbsp;const</tt>
  132. or <tt>typedef</tt> and/or pass the files through an external
  133. C&nbsp;pre-processor (once). Be careful not to include unneeded or
  134. redundant declarations from unrelated header files.
  135. </p>
  136. <h3 id="ffi_C"><tt>ffi.C</tt></h3>
  137. <p>
  138. This is the default C&nbsp;library namespace &mdash; note the
  139. uppercase <tt>'C'</tt>. It binds to the default set of symbols or
  140. libraries on the target system. These are more or less the same as a
  141. C&nbsp;compiler would offer by default, without specifying extra link
  142. libraries.
  143. </p>
  144. <p>
  145. On POSIX systems, this binds to symbols in the default or global
  146. namespace. This includes all exported symbols from the executable and
  147. any libraries loaded into the global namespace. This includes at least
  148. <tt>libc</tt>, <tt>libm</tt>, <tt>libdl</tt> (on Linux),
  149. <tt>libgcc</tt> (if compiled with GCC), as well as any exported
  150. symbols from the Lua/C&nbsp;API provided by LuaJIT itself.
  151. </p>
  152. <p>
  153. On Windows systems, this binds to symbols exported from the
  154. <tt>*.exe</tt>, the <tt>lua51.dll</tt> (i.e. the Lua/C&nbsp;API
  155. provided by LuaJIT itself), the C&nbsp;runtime library LuaJIT was linked
  156. with (<tt>msvcrt*.dll</tt>), <tt>kernel32.dll</tt>,
  157. <tt>user32.dll</tt> and <tt>gdi32.dll</tt>.
  158. </p>
  159. <h3 id="ffi_load"><tt>clib = ffi.load(name [,global])</tt></h3>
  160. <p>
  161. This loads the dynamic library given by <tt>name</tt> and returns
  162. a new C&nbsp;library namespace which binds to its symbols. On POSIX
  163. systems, if <tt>global</tt> is <tt>true</tt>, the library symbols are
  164. loaded into the global namespace, too.
  165. </p>
  166. <p>
  167. If <tt>name</tt> is a path, the library is loaded from this path.
  168. Otherwise <tt>name</tt> is canonicalized in a system-dependent way and
  169. searched in the default search path for dynamic libraries:
  170. </p>
  171. <p>
  172. On POSIX systems, if the name contains no dot, the extension
  173. <tt>.so</tt> is appended. Also, the <tt>lib</tt> prefix is prepended
  174. if necessary. So <tt>ffi.load("z")</tt> looks for <tt>"libz.so"</tt>
  175. in the default shared library search path.
  176. </p>
  177. <p>
  178. On Windows systems, if the name contains no dot, the extension
  179. <tt>.dll</tt> is appended. So <tt>ffi.load("ws2_32")</tt> looks for
  180. <tt>"ws2_32.dll"</tt> in the default DLL search path.
  181. </p>
  182. <h2 id="create">Creating cdata Objects</h2>
  183. <p>
  184. The following API functions create cdata objects (<tt>type()</tt>
  185. returns <tt>"cdata"</tt>). All created cdata objects are
  186. <a href="ext_ffi_semantics.html#gc">garbage collected</a>.
  187. </p>
  188. <h3 id="ffi_new"><tt>cdata = ffi.new(ct [,nelem] [,init...])<br>
  189. cdata = <em>ctype</em>([nelem,] [init...])</tt></h3>
  190. <p>
  191. Creates a cdata object for the given <tt>ct</tt>. VLA/VLS types
  192. require the <tt>nelem</tt> argument. The second syntax uses a ctype as
  193. a constructor and is otherwise fully equivalent.
  194. </p>
  195. <p>
  196. The cdata object is initialized according to the
  197. <a href="ext_ffi_semantics.html#init">rules for initializers</a>,
  198. using the optional <tt>init</tt> arguments. Excess initializers cause
  199. an error.
  200. </p>
  201. <p>
  202. Performance notice: if you want to create many objects of one kind,
  203. parse the cdecl only once and get its ctype with
  204. <tt>ffi.typeof()</tt>. Then use the ctype as a constructor repeatedly.
  205. </p>
  206. <p style="font-size: 8pt;">
  207. Please note that an anonymous <tt>struct</tt> declaration implicitly
  208. creates a new and distinguished ctype every time you use it for
  209. <tt>ffi.new()</tt>. This is probably <b>not</b> what you want,
  210. especially if you create more than one cdata object. Different anonymous
  211. <tt>structs</tt> are not considered assignment-compatible by the
  212. C&nbsp;standard, even though they may have the same fields! Also, they
  213. are considered different types by the JIT-compiler, which may cause an
  214. excessive number of traces. It's strongly suggested to either declare
  215. a named <tt>struct</tt> or <tt>typedef</tt> with <tt>ffi.cdef()</tt>
  216. or to create a single ctype object for an anonymous <tt>struct</tt>
  217. with <tt>ffi.typeof()</tt>.
  218. </p>
  219. <h3 id="ffi_typeof"><tt>ctype = ffi.typeof(ct)</tt></h3>
  220. <p>
  221. Creates a ctype object for the given <tt>ct</tt>.
  222. </p>
  223. <p>
  224. This function is especially useful to parse a cdecl only once and then
  225. use the resulting ctype object as a <a href="#ffi_new">constructor</a>.
  226. </p>
  227. <h3 id="ffi_cast"><tt>cdata = ffi.cast(ct, init)</tt></h3>
  228. <p>
  229. Creates a scalar cdata object for the given <tt>ct</tt>. The cdata
  230. object is initialized with <tt>init</tt> using the "cast" variant of
  231. the <a href="ext_ffi_semantics.html#convert">C&nbsp;type conversion
  232. rules</a>.
  233. </p>
  234. <p>
  235. This functions is mainly useful to override the pointer compatibility
  236. checks or to convert pointers to addresses or vice versa.
  237. </p>
  238. <h3 id="ffi_metatype"><tt>ctype = ffi.metatype(ct, metatable)</tt></h3>
  239. <p>
  240. Creates a ctype object for the given <tt>ct</tt> and associates it with
  241. a metatable. Only <tt>struct</tt>/<tt>union</tt> types, complex numbers
  242. and vectors are allowed. Other types may be wrapped in a
  243. <tt>struct</tt>, if needed.
  244. </p>
  245. <p>
  246. The association with a metatable is permanent and cannot be changed
  247. afterwards. Neither the contents of the <tt>metatable</tt> nor the
  248. contents of an <tt>__index</tt> table (if any) may be modified
  249. afterwards. The associated metatable automatically applies to all uses
  250. of this type, no matter how the objects are created or where they
  251. originate from. Note that pre-defined operations on types have
  252. precedence (e.g. declared field names cannot be overriden).
  253. </p>
  254. <p>
  255. All standard Lua metamethods are implemented. These are called directly,
  256. without shortcuts and on any mix of types. For binary operations, the
  257. left operand is checked first for a valid ctype metamethod. The
  258. <tt>__gc</tt> metamethod only applies to <tt>struct</tt>/<tt>union</tt>
  259. types and performs an implicit <a href="#ffi_gc"><tt>ffi.gc()</tt></a>
  260. call during creation of an instance.
  261. </p>
  262. <h3 id="ffi_gc"><tt>cdata = ffi.gc(cdata, finalizer)</tt></h3>
  263. <p>
  264. Associates a finalizer with a pointer or aggregate cdata object. The
  265. cdata object is returned unchanged.
  266. </p>
  267. <p>
  268. This function allows safe integration of unmanaged resources into the
  269. automatic memory management of the LuaJIT garbage collector. Typical
  270. usage:
  271. </p>
  272. <pre class="code">
  273. local p = ffi.gc(ffi.C.malloc(n), ffi.C.free)
  274. ...
  275. p = nil -- Last reference to p is gone.
  276. -- GC will eventually run finalizer: ffi.C.free(p)
  277. </pre>
  278. <p>
  279. A cdata finalizer works like the <tt>__gc</tt> metamethod for userdata
  280. objects: when the last reference to a cdata object is gone, the
  281. associated finalizer is called with the cdata object as an argument. The
  282. finalizer can be a Lua function or a cdata function or cdata function
  283. pointer. An existing finalizer can be removed by setting a <tt>nil</tt>
  284. finalizer, e.g. right before explicitly deleting a resource:
  285. </p>
  286. <pre class="code">
  287. ffi.C.free(ffi.gc(p, nil)) -- Manually free the memory.
  288. </pre>
  289. <h2 id="info">C&nbsp;Type Information</h2>
  290. <p>
  291. The following API functions return information about C&nbsp;types.
  292. They are most useful for inspecting cdata objects.
  293. </p>
  294. <h3 id="ffi_sizeof"><tt>size = ffi.sizeof(ct [,nelem])</tt></h3>
  295. <p>
  296. Returns the size of <tt>ct</tt> in bytes. Returns <tt>nil</tt> if
  297. the size is not known (e.g. for <tt>"void"</tt> or function types).
  298. Requires <tt>nelem</tt> for VLA/VLS types, except for cdata objects.
  299. </p>
  300. <h3 id="ffi_alignof"><tt>align = ffi.alignof(ct)</tt></h3>
  301. <p>
  302. Returns the minimum required alignment for <tt>ct</tt> in bytes.
  303. </p>
  304. <h3 id="ffi_offsetof"><tt>ofs [,bpos,bsize] = ffi.offsetof(ct, field)</tt></h3>
  305. <p>
  306. Returns the offset (in bytes) of <tt>field</tt> relative to the start
  307. of <tt>ct</tt>, which must be a <tt>struct</tt>. Additionally returns
  308. the position and the field size (in bits) for bit fields.
  309. </p>
  310. <h3 id="ffi_istype"><tt>status = ffi.istype(ct, obj)</tt></h3>
  311. <p>
  312. Returns <tt>true</tt> if <tt>obj</tt> has the C&nbsp;type given by
  313. <tt>ct</tt>. Returns <tt>false</tt> otherwise.
  314. </p>
  315. <p>
  316. C&nbsp;type qualifiers (<tt>const</tt> etc.) are ignored. Pointers are
  317. checked with the standard pointer compatibility rules, but without any
  318. special treatment for <tt>void&nbsp;*</tt>. If <tt>ct</tt> specifies a
  319. <tt>struct</tt>/<tt>union</tt>, then a pointer to this type is accepted,
  320. too. Otherwise the types must match exactly.
  321. </p>
  322. <p>
  323. Note: this function accepts all kinds of Lua objects for the
  324. <tt>obj</tt> argument, but always returns <tt>false</tt> for non-cdata
  325. objects.
  326. </p>
  327. <h2 id="util">Utility Functions</h2>
  328. <h3 id="ffi_errno"><tt>err = ffi.errno([newerr])</tt></h3>
  329. <p>
  330. Returns the error number set by the last C&nbsp;function call which
  331. indicated an error condition. If the optional <tt>newerr</tt> argument
  332. is present, the error number is set to the new value and the previous
  333. value is returned.
  334. </p>
  335. <p>
  336. This function offers a portable and OS-independent way to get and set the
  337. error number. Note that only <em>some</em> C&nbsp;functions set the error
  338. number. And it's only significant if the function actually indicated an
  339. error condition (e.g. with a return value of <tt>-1</tt> or
  340. <tt>NULL</tt>). Otherwise, it may or may not contain any previously set
  341. value.
  342. </p>
  343. <p>
  344. You're advised to call this function only when needed and as close as
  345. possible after the return of the related C&nbsp;function. The
  346. <tt>errno</tt> value is preserved across hooks, memory allocations,
  347. invocations of the JIT compiler and other internal VM activity. The same
  348. applies to the value returned by <tt>GetLastError()</tt> on Windows, but
  349. you need to declare and call it yourself.
  350. </p>
  351. <h3 id="ffi_string"><tt>str = ffi.string(ptr [,len])</tt></h3>
  352. <p>
  353. Creates an interned Lua string from the data pointed to by
  354. <tt>ptr</tt>.
  355. </p>
  356. <p>
  357. If the optional argument <tt>len</tt> is missing, <tt>ptr</tt> is
  358. converted to a <tt>"char&nbsp;*"</tt> and the data is assumed to be
  359. zero-terminated. The length of the string is computed with
  360. <tt>strlen()</tt>.
  361. </p>
  362. <p>
  363. Otherwise <tt>ptr</tt> is converted to a <tt>"void&nbsp;*"</tt> and
  364. <tt>len</tt> gives the length of the data. The data may contain
  365. embedded zeros and need not be byte-oriented (though this may cause
  366. endianess issues).
  367. </p>
  368. <p>
  369. This function is mainly useful to convert (temporary)
  370. <tt>"const&nbsp;char&nbsp;*"</tt> pointers returned by
  371. C&nbsp;functions to Lua strings and store them or pass them to other
  372. functions expecting a Lua string. The Lua string is an (interned) copy
  373. of the data and bears no relation to the original data area anymore.
  374. Lua strings are 8&nbsp;bit clean and may be used to hold arbitrary,
  375. non-character data.
  376. </p>
  377. <p>
  378. Performance notice: it's faster to pass the length of the string, if
  379. it's known. E.g. when the length is returned by a C&nbsp;call like
  380. <tt>sprintf()</tt>.
  381. </p>
  382. <h3 id="ffi_copy"><tt>ffi.copy(dst, src, len)<br>
  383. ffi.copy(dst, str)</tt></h3>
  384. <p>
  385. Copies the data pointed to by <tt>src</tt> to <tt>dst</tt>.
  386. <tt>dst</tt> is converted to a <tt>"void&nbsp;*"</tt> and <tt>src</tt>
  387. is converted to a <tt>"const void&nbsp;*"</tt>.
  388. </p>
  389. <p>
  390. In the first syntax, <tt>len</tt> gives the number of bytes to copy.
  391. Caveat: if <tt>src</tt> is a Lua string, then <tt>len</tt> must not
  392. exceed <tt>#src+1</tt>.
  393. </p>
  394. <p>
  395. In the second syntax, the source of the copy must be a Lua string. All
  396. bytes of the string <em>plus a zero-terminator</em> are copied to
  397. <tt>dst</tt> (i.e. <tt>#src+1</tt> bytes).
  398. </p>
  399. <p>
  400. Performance notice: <tt>ffi.copy()</tt> may be used as a faster
  401. (inlinable) replacement for the C&nbsp;library functions
  402. <tt>memcpy()</tt>, <tt>strcpy()</tt> and <tt>strncpy()</tt>.
  403. </p>
  404. <h3 id="ffi_fill"><tt>ffi.fill(dst, len [,c])</tt></h3>
  405. <p>
  406. Fills the data pointed to by <tt>dst</tt> with <tt>len</tt> constant
  407. bytes, given by <tt>c</tt>. If <tt>c</tt> is omitted, the data is
  408. zero-filled.
  409. </p>
  410. <p>
  411. Performance notice: <tt>ffi.fill()</tt> may be used as a faster
  412. (inlinable) replacement for the C&nbsp;library function
  413. <tt>memset(dst,&nbsp;c,&nbsp;len)</tt>. Please note the different
  414. order of arguments!
  415. </p>
  416. <h2 id="target">Target-specific Information</h2>
  417. <h3 id="ffi_abi"><tt>status = ffi.abi(param)</tt></h3>
  418. <p>
  419. Returns <tt>true</tt> if <tt>param</tt> (a Lua string) applies for the
  420. target ABI (Application Binary Interface). Returns <tt>false</tt>
  421. otherwise. The following parameters are currently defined:
  422. </p>
  423. <table class="abitable">
  424. <tr class="abihead">
  425. <td class="abiparam">Parameter</td>
  426. <td class="abidesc">Description</td>
  427. </tr>
  428. <tr class="odd separate">
  429. <td class="abiparam">32bit</td><td class="abidesc">32 bit architecture</td></tr>
  430. <tr class="even">
  431. <td class="abiparam">64bit</td><td class="abidesc">64 bit architecture</td></tr>
  432. <tr class="odd separate">
  433. <td class="abiparam">le</td><td class="abidesc">Little-endian architecture</td></tr>
  434. <tr class="even">
  435. <td class="abiparam">be</td><td class="abidesc">Big-endian architecture</td></tr>
  436. <tr class="odd separate">
  437. <td class="abiparam">fpu</td><td class="abidesc">Target has a hardware FPU</td></tr>
  438. <tr class="even">
  439. <td class="abiparam">softfp</td><td class="abidesc">softfp calling conventions</td></tr>
  440. <tr class="odd">
  441. <td class="abiparam">hardfp</td><td class="abidesc">hardfp calling conventions</td></tr>
  442. <tr class="even separate">
  443. <td class="abiparam">eabi</td><td class="abidesc">EABI variant of the standard ABI</td></tr>
  444. <tr class="odd">
  445. <td class="abiparam">win</td><td class="abidesc">Windows variant of the standard ABI</td></tr>
  446. </table>
  447. <h3 id="ffi_os"><tt>ffi.os</tt></h3>
  448. <p>
  449. Contains the target OS name. Same contents as
  450. <a href="ext_jit.html#jit_os"><tt>jit.os</tt></a>.
  451. </p>
  452. <h3 id="ffi_arch"><tt>ffi.arch</tt></h3>
  453. <p>
  454. Contains the target architecture name. Same contents as
  455. <a href="ext_jit.html#jit_arch"><tt>jit.arch</tt></a>.
  456. </p>
  457. <h2 id="callback">Methods for Callbacks</h2>
  458. <p>
  459. The C&nbsp;types for <a href="ext_ffi_semantics.html#callback">callbacks</a>
  460. have some extra methods:
  461. </p>
  462. <h3 id="callback_free"><tt>cb:free()</tt></h3>
  463. <p>
  464. Free the resources associated with a callback. The associated Lua
  465. function is unanchored and may be garbage collected. The callback
  466. function pointer is no longer valid and must not be called anymore
  467. (it may be reused by a subsequently created callback).
  468. </p>
  469. <h3 id="callback_set"><tt>cb:set(func)</tt></h3>
  470. <p>
  471. Associate a new Lua function with a callback. The C&nbsp;type of the
  472. callback and the callback function pointer are unchanged.
  473. </p>
  474. <p>
  475. This method is useful to dynamically switch the receiver of callbacks
  476. without creating a new callback each time and registering it again (e.g.
  477. with a GUI library).
  478. </p>
  479. <h2 id="extended">Extended Standard Library Functions</h2>
  480. <p>
  481. The following standard library functions have been extended to work
  482. with cdata objects:
  483. </p>
  484. <h3 id="tonumber"><tt>n = tonumber(cdata)</tt></h3>
  485. <p>
  486. Converts a number cdata object to a <tt>double</tt> and returns it as
  487. a Lua number. This is particularly useful for boxed 64&nbsp;bit
  488. integer values. Caveat: this conversion may incur a precision loss.
  489. </p>
  490. <h3 id="tostring"><tt>s = tostring(cdata)</tt></h3>
  491. <p>
  492. Returns a string representation of the value of 64&nbsp;bit integers
  493. (<tt><b>"</b>nnn<b>LL"</b></tt> or <tt><b>"</b>nnn<b>ULL"</b></tt>) or
  494. complex numbers (<tt><b>"</b>re&plusmn;im<b>i"</b></tt>). Otherwise
  495. returns a string representation of the C&nbsp;type of a ctype object
  496. (<tt><b>"ctype&lt;</b>type<b>&gt;"</b></tt>) or a cdata object
  497. (<tt><b>"cdata&lt;</b>type<b>&gt;:&nbsp;</b>address"</tt>), unless you
  498. override it with a <tt>__tostring</tt> metamethod (see
  499. <a href="#ffi_metatype"><tt>ffi.metatype()</tt></a>).
  500. </p>
  501. <h3 id="pairs"><tt>iter, obj, start = pairs(cdata)<br>
  502. iter, obj, start = ipairs(cdata)<br></tt></h3>
  503. <p>
  504. Calls the <tt>__pairs</tt> or <tt>__ipairs</tt> metamethod of the
  505. corresponding ctype.
  506. </p>
  507. <h2 id="literals">Extensions to the Lua Parser</h2>
  508. <p>
  509. The parser for Lua source code treats numeric literals with the
  510. suffixes <tt>LL</tt> or <tt>ULL</tt> as signed or unsigned 64&nbsp;bit
  511. integers. Case doesn't matter, but uppercase is recommended for
  512. readability. It handles both decimal (<tt>42LL</tt>) and hexadecimal
  513. (<tt>0x2aLL</tt>) literals.
  514. </p>
  515. <p>
  516. The imaginary part of complex numbers can be specified by suffixing
  517. number literals with <tt>i</tt> or <tt>I</tt>, e.g. <tt>12.5i</tt>.
  518. Caveat: you'll need to use <tt>1i</tt> to get an imaginary part with
  519. the value one, since <tt>i</tt> itself still refers to a variable
  520. named <tt>i</tt>.
  521. </p>
  522. <br class="flush">
  523. </div>
  524. <div id="foot">
  525. <hr class="hide">
  526. Copyright &copy; 2005-2012 Mike Pall
  527. <span class="noprint">
  528. &middot;
  529. <a href="contact.html">Contact</a>
  530. </span>
  531. </div>
  532. </body>
  533. </html>